1. Field
The present invention generally relates to the field of communications, and more specifically, to communications in a cellular communication system.
2. Background
A cellular communication system may operate in accordance with code division multiple access (CDMA) communication technique. Several CDMA systems have been in commercial operation for a number of years. In CDMA communication systems, a number of users in the same geographical area may choose to operate on a common carrier frequency. The signal from each user is encoded according to a unique assigned code. A receiver decodes each signal according to the assigned code. A receiver may receive signals from different users with a common carrier frequency. While a signal for one user is being decoded, the signals transmitted from all other users may be treated as interference. Excessive transmission by different users may cause interference for other users in addition to causing system overload at a base station. When a base station is overloaded it must reject a portion of the incoming call requests.
Rejecting a call request has several negative effects. One effect in particular is the amount of processing and bandwidth at the base station allocated to process a rejected call. Another effect is use of the mobile station power to initiate such a call request without success. Moreover, during a call request attempt, the mobile station may gradually increase its transmit power level which can affect communications of other mobile stations.
In certain situations, more mobile stations may attempt to access the base station than the number of available channels, i.e. the base station is overloaded. This may be the case when the mobile station traffic surges for unanticipated reasons or when the base station is damaged in some way and exhibits decreased capabilities for a period of time. Users whose call requests are rejected or not allowed by the base station will usually keep re-trying their call until accepted by the base station. The group of rejected or re-trying callers that accumulates during this period is referred to as the xe2x80x9cbackloggedxe2x80x9d users, and the corresponding rejected call requests are referred to as the base station""s xe2x80x9cbacklogxe2x80x9d. When the base station is repaired and put back online, for example, there will be backlogged users attempting to make calls in addition to the usual number of expected new calls. If the base station is not equipped to handle this combined load, many of the call requests may be rejected.
Thus, there is a need in the art for effective means for depleting backlog in a communication system.
Embodiments disclosed herein address the above stated needs by gradually depleting backlog at a base station, utilizing a blocking probability generated from an initial parameter set.
In one aspect of the invention, an initial parameter set providing an initial blocking probability and a timestamp is received. Once the initial parameter set has been received, a current time index is determined based on the timestamp. Following, a current blocking probability is calculated based on the initial blocking probability and the current time index. After the current blocking probability has been calculated, a random number between 0 and 1 is generated and compared to the current blocking probability. A call request is blocked, for example, when the random number is less than the current blocking probability.
In another aspect of the invention, the initial parameter set also provides a delay period, a throughput rate, an expected new call rate and an initial backlog. The initial blocking probability is then determined from the throughput rate, the expected new call rate and the initial backlog. Subsequently, an elapsed time between the timestamp and the current system time is determined, and a current time index is determined by dividing the elapsed time by the delay period. Thereafter, a random number between 0 and 1 is generated, and call request is blocked, for example, when the random number is less than the current blocking probability.